Bump rubocop-ast from 1.30.0 to 1.31.0 (#48)

Bumps [rubocop-ast](https://github.com/rubocop/rubocop-ast) from 1.30.0 to 1.31.0.
- [Release notes](https://github.com/rubocop/rubocop-ast/releases)
- [Changelog](https://github.com/rubocop/rubocop-ast/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop-ast@v1.30.0...v1.31.0)

---
updated-dependencies:
- dependency-name: rubocop-ast
  dependency-type: indirect
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>